The present invention relates to a lane-keeping control of a lane-keeping support system that is intended to assist the driver steering action.
Considerable research has been done in recent years on lane-keeping support (LKS) systems for reducing drivers"" workload. Such a LKS system certainly assists a driver in steering a moving vehicle to track or follow a contrived centerline between lane markings of a roadway by applying a steering bias to a steering system of the vehicle. The steering bias is provided by a servo system, and it may either assist or oppose steering torque from the driver in lane-keeping control (LKC) mode. In order for the servo system to provide such a steering bias, it is the common practice to use the steering wheel angle as a control input to the servo system. This approach provides superior robustness because the non-linearity of steering system is compensated for. However, it does not readily allow driver steering intervention. The driver steering intervention may be recognized in various manners, and the recognition is accompanied by a transient control to allow smooth shift from LKC mode to normal driver control (NDC) mode.
In order to recognize such driver steering intervention, various methods have been previously known in the art. One such example is described in JP-A 11-286280, according to which, in LKC mode, an actual value of steering torque from the driver, detected at a torque sensor, is being compared to a threshold value. The threshold value is expressed as the product of a predetermined value and the maximum of the previously monitored actual values of steering torque from the driver in NDC mode. The driver steering intervention is recognized when the threshold value is exceeded. Another example, which is also described in JP-A 11-286280, is comparing a deviation between an actual value of steering angle, detected at a steering angle sensor, and a target value thereof to a threshold value. The target value indicates a steering angle with which a vehicle may be directed toward the contrived centerline between lane markings. The driver intervention is recognized when the threshold value is exceeded.
The above-mentioned technologies, however, posses their own distinct disadvantages. Comparing the actual value of steering torque to the threshold value requires the additional provision of a torque sensor. The addition of a torque sensor is difficult to suppress increase of cost and installation space. On other hand, comparing the deviation in steering angle to a threshold value, although it does not require a new sensor, has its disadvantage that the threshold value is difficult to set. This difficultly derives from the unlikelihood of occurrence of deviation due to the property of a servo control that the deviation in steering angle is reduced toward zero. Therefore, there is a need for an alternative approach to the recognition of driver intervention, which does not require a torque sensor and, therefore, is economical to install and maintain.
An object of the present invention is to provide for lane-keeping control, which satisfies the above-mentioned need.
This object has been achieved, according to the present invention, by a method for lane-keeping control of a lane-keeping support system for assisting the driver steering action of a vehicle in following a target line between lane markings on a roadway, the method comprising:
producing a command indicative of steering torque assist needed to steer a vehicle in following a target line between lane markings on a roadway during driving in lane-keeping control (LKC) mode;
providing a map having two sets of limit data against a range of values of lateral acceleration to which the vehicle is subject, between which sets of limit data there is a range of values of the command during various phases of steering the vehicle to turn in the LKC mode;
correcting the two sets of limit data in a manner to compensate for undesired effect caused by any deviation of the range of values of the command due to the presence of continuous disturbance; and
comparing the instantaneous value of the command to two limit values established out of the corrected two sets of limit data in determining whether or not there is driver steering intervention.